Fuel injection system and method for injection

ABSTRACT

A fuel injection system for internal combustion engines has at least one fuel injector which injects fuel into a combustion chamber delimited by a cylinder wall in which a piston is guided, and it has a spark plug which protrudes into the combustion space, and the fuel injector is designed so that a conical spray jet is produced in the combustion chamber. The conical spray jet has an angle cutout in the area of the spark plug.

FIELD OF THE INVENTION

The present invention relates to a fuel injection system and a method ofinjection.

BACKGROUND INFORMATION

In internal combustion engines having spark ignition of a compressedfuel mixture with internal formation of the mixture, a “mixture cloud”which must have a certain fuel-air ratio in the ignitable range isrequired for stratified charge operation in the spark plug area. To thisend, fuel injectors having nozzles which open toward the inside or theoutside and produce a conical jet are used.

For example, German Published Patent Application No. 198 04 463describes a fuel injection system for internal combustion engines havingspark ignition of a compressed fuel mixture; this fuel injection systemis provided with at least one fuel injector which injects fuel into acombustion chamber formed by a piston/cylinder arrangement and isequipped with a spark plug projecting into the combustion chamber. Thefuel injector is provided with at least one row of injection holesdistributed over the circumference of a nozzle body of the fuelinjector. Through controlled injection of fuel through the injectionholes, a jet-guided combustion method is implemented by the formation ofa mixture cloud, at least one jet being directed in the direction of thespark plug. Other jets ensure that an at least approximately closed orcoherent mixture cloud is formed.

German Patent No. 196 42 653 describes a method of forming an ignitablefuel-air mixture. An ignitable fuel-air mixture is formable in thecylinders of direct injection internal combustion engines, in that fuelis injected into each combustion chamber delimited by a piston, by wayof an injector on opening of a nozzle orifice due to a valve elementbeing lifted up from a valve seat surrounding the nozzle orifice. Topermit formation of a mixture optimized for fuel consumption andemissions in each operating point of the entire engine characteristicsmap under all operating conditions of the internal combustion engine, inparticular in stratified charge operation, the opening stroke of thevalve element and the injection time are adjustable.

German Patent No. 38 08 635 describes a fuel injection device for directinjection of fuel into the cylinder of an internal combustion enginehaving compression of a fuel mixture. The fuel injection device includesa fuel injector which is situated in the cylinder wall at a distancefrom the cylinder head and opposite the exhaust opening and which has anoutlet opening, with the axis of the jet of the injection valve beingdirected at the area around the spark plug situated in the cylinderhead. The fuel injector here has a magnetically operated valve needlehaving helical swirl grooves to produce a swirl flow of the injectionjet. The total cross-sectional area of the swirl grooves is smaller byat least one half than the cross-sectional area of the outlet opening,the fuel injector being situated above the flushing opening, and withits jet axis directed at the ignition point situated at the center ofthe cylinder head.

Most injection systems known from the publications cited above concerncombustion methods with wall-guided fuel flow. This combustion methoddepends to a very great extent on the movement of incoming air which hasthe function of conveying an ignitable fuel-air mixture exactly into theelectrode area of the spark plug over the entire stratified chargeoperation range of the engine characteristics map. In the wall-guidedcombustion method, fuel is carried to the spark plug with the support ofmore or less fractured combustion chamber geometries with simultaneousformation of the mixture.

Transport of the mixture to the spark plug is very incomplete inwall-guided and air-guided combustion methods in idling operation and inthe lower partial load range, and in the middle partial load range ofoperation, it is possible in part only with unjustifiably lowmanufacturing tolerances of the high-pressure injectors used or the flowguidance through the intake manifold. The inadequate reproducibility isapparent in particular in increased emission of unburned hydrocarbonsdue to isolated instances of misfiring. These properties result inanother serious disadvantage of the two combustion methods mentionedabove: the engine cannot be operated unthrottled in the idling and lowerpartial load ranges because due to the great distance between the fuelinjector and the spark plug, smaller injection quantities no longerreach the spark plug in the mixture concentration required for stablecombustion. This means that the fuel-air mixture at the spark plugelectrodes becomes too lean. However, the consumption advantage isreduced in comparison with internal combustion engines havingcompression of a mixture with spark ignition and intake manifoldinjection due to the intake air throttling.

SUMMARY OF THE INVENTION

The fuel injection system according to the present invention and themethod according to the present invention have the advantage over therelated art that the mixture in the area of the spark plug is not toorich due to the angle cutout.

It is also advantageous that the spark plugs do not develop as muchsoot, thermal shock load is reduced, and there is an improvement in thelack of sensitivity to the firing angle with a fixed injection time inthe entire engine characteristics map in which stratified chargeoperation is carried out. Injection and ignition (or vice versa) maytake place simultaneously.

It is also advantageous that the spark cannot be blown out due to thehigh injection rate because the droplet speed is greatest at the centerof the jet, and on the angle bisectors of the two injection jetsbordering the spark plug area, the spark conforms exactly torequirements regarding the quality of the fuel-air mixture and the rateof flow.

It is also advantageous that the depth of installation sensitivity ofthe spark plug is lower.

The injection jet is advantageously formed using a plurality ofinjection holes. Injection holes may be situated to advantage in severaloffset rows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic axial section through an embodiment of a fuelinjection system according to the present invention.

FIG. 2 shows the section labeled as II—II in FIG. 1 through the cylinderhead of the embodiment of the fuel injection system according to thepresent invention as illustrated in FIG. 1.

FIG. 3 shows a schematic diagram of a first jet pattern produced by thefuel injection system according to the present invention.

FIG. 4A shows a first illustration of a schematic diagram of a secondjet pattern produced by another embodiment of the fuel injection systemaccording to the present invention.

FIG. 4B shows a second illustration of a schematic diagram of a secondjet pattern produced by another embodiment of the fuel injection systemaccording to the present invention.

FIG. 4C shows the arrangement of injection holes to produce the jetpatterns.

FIG. 5A shows a first diagram of the emissions of hydrocarbons andnitrogen oxide and the specific fuel consumption, each shown for a fuelinjection system with and without the angle cutout according to thepresent invention for the spark plugs.

FIG. 5B shows a second diagram of the emissions of hydrocarbons andnitrogen oxide and the specific fuel consumption, each shown for a fuelinjection system with and without the angle cutout according to thepresent invention for the spark plugs.

FIG. 5C shows a third diagram of the emissions of hydrocarbons andnitrogen oxide and the specific fuel consumption, each shown for a fuelinjection system with and without the angle cutout according to thepresent invention for the spark plugs.

DETAILED DESCRIPTION

FIG. 1 shows a detail of a sectional diagram of one embodiment of thefuel injection system according to the present invention.

Fuel injection system 1 includes a cylinder block having a cylinder wall2 in which a piston 3 is guided. Piston 3 is guided up and down by aconnecting rod 4 on cylinder wall 2. Cylinder wall 2 is closed at oneend by a cylinder head 5. Cylinder wall 2, piston 3 and cylinder head 5enclose a combustion chamber 6.

A fuel injection valve 7 is situated preferably centrally in cylinderhead 5. A spark plug 8 is inserted into a borehole in cylinder head 5with a slight lateral offset. In addition, at least one intake valve 9and at least one outlet valve 10 are also provided. The arrangement offuel injector 7, spark plug 8, intake valve 9 and outlet valve 10 isshown in greater detail in FIG. 2.

In the case of fuel injection system 1 which is in operation, a conicaljet of fuel is sprayed into combustion chamber 6 through boreholesprovided in fuel injector 7. A mixture cloud 11 is formed by mixing fueland air in combustion chamber 6. Mixture cloud 11 is ignited by sparkplug 8. The shape of the conical jet and the recess on spark plug 8according to the present invention are described in greater detail withreference to FIGS. 3 and 4.

FIG. 2 shows a section along line II—II in FIG. 1 through the embodimentof fuel injection system 1 according to the present invention asillustrated in FIG. 1. Fuel injector 7 is situated centrally in a recess12 in cylinder head 5. Spark plug 8 is situated in a triangle formed byfuel injector 7 and two outlet valves 10. Two intake valves 9 aresituated symmetrically with outlet valves 10. Intake and outlet valves9, 10 may also be situated with the sides switched or in a crosspattern.

FIG. 3 shows schematically a jet pattern of fuel injector 7 producing aconical jet of fuel. Fuel injector 7 is situated at the center of thecircle indicating lateral surface 13 of the cone. Since fuel injector 7is designed as a multi-hole fuel injector, multiple injection jets 14are sprayed into combustion chamber 6. Injection jets 14 are representedsymbolically as arrows directed outward. In the present embodiment, thisis a fuel injector 7 having thirteen injection holes 16 producingthirteen injection jets 14 accordingly. Individual injection jets 14 areseparated from one another by an angular distance β which amounts to 26°in the present embodiment. This does not include injection jets 14 awhich are injected at the right and left of spark plug 8. Angle α of anangle cutout 17 between injection jets 14 a enclosing spark plug 8amounts to 30° to 60° or in the present embodiment 45°. Spark plug 8 issituated on an angle bisector 18 of angle α. This arrangement preventsspark plug 8 from being sprayed directly by injection jets 14 and 14 aand therefore carbonization of spark plug 8 can be reduced significantlyand the lifetime of spark plug 8 can be prolonged.

FIGS. 4A and 4B show the jet pattern of a second embodiment of fuelinjection system 1.

FIG. 4A shows the jet pattern in a top view like that in FIG. 3. Fuelinjector 7 is located at the center of the circle representing conicallateral surface 13. In this case, mixture cloud 11 is produced by twodifferent conical lateral surfaces 13 a and 13 b. Angle α of anglecutout 17 between injection jets 14 a enclosing spark plug 8 againamounts to approximately 45°. Angle β between two injection jets 14which are outside and adjacent to angle section 17, but in thisembodiment are located in two different planes, amounts to approximately20°.

FIG. 4B illustrates two conical lateral surfaces 13 a and 13 b, which inthis embodiment are covered by a total of seventeen injection holes. Thecone angle of internal conical lateral surface 13 b is 90°, while thecone angle of external conical lateral surface 13 a amounts to 110°.Internal conical lateral surface 13 b is covered by eight injection jets14 while outer conical lateral surface 13 a is covered by nine injectionjets 14. This produces a largely homogeneous mixture cloud 11 which doesnot have any lean pockets.

FIG. 4C shows a nozzle body 15 of multi-hole fuel injector 7 in aschematic diagram. The injection hole arrangement of nozzle body 15 isshown in a developed view at the side. To create a 45° angle cutout 17,all that is necessary in this embodiment is to omit one of injectionholes 16 situated in a first annular row 19 b, forming internal conicallateral surface 13 b. This in turn produces an angle cutout 17 whichmakes it possible to operate fuel injector 7 without directly sprayingfuel onto spark plug 8. Conversely, a gap may also be provided in thearrangement of injection holes 16 of a second annular row 19 a,producing outer conical lateral surface 13 a.

FIGS. 5A-5C show diagrams of hydrocarbon and nitrogen oxide emissionsand the specific fuel consumption for a fuel injection system with andwithout angle cutout 17 for spark plug 8. The consumption and emissionvalues are plotted here as a function of the firing angle in units ofthe crank angle, measured on the crankshaft. The curve shown with asolid line represents measurement results for a fuel injection systemwithout an angle cutout for the spark plug, and the curve shown with abroken line with asterisks represents the measurement results for a fuelinjection system having an angle cutout for the spark plug.

In general, the diagrams in FIGS. 5A-5C show that the jet-guidedcombustion method is independent of the firing angle to a great extent.

FIG. 5A shows the hydrocarbon emissions in volume units for therespective injection systems as a function of the firing angle. Thehydrocarbon emissions decrease significantly when using a fuel injectionsystem having an angle cutout for the spark plug, in some cases as muchas 50% in comparison with emissions in operation of a fuel injectionsystem without an angle cutout for the spark plug.

FIG. 5B shows a corresponding diagram for the nitrogen oxides emissions,also plotted in volume units as a function of the firing angle. Theemission values for nitrogen oxides remain almost the same for both fuelinjection systems over the firing angle curve.

FIG. 5C shows the specific fuel consumption for the various fuelinjection systems in units of grams per kilowatt hours as a function ofthe firing angle. Here again, a considerable improvement in consumptionvalues can be achieved by using a fuel injection system having an anglecutout for the spark plug, the reduction in consumption amounting to asmuch as 15% in some cases. The present invention is not limited to theembodiments presented here and in particular it can also be applied tomulti-hole fuel injectors having fewer or more injection holes.Likewise, the injection jets may be situated on more than two spraycircles (rows) to thereby improve the homogeneity of the fuel-airmixture.

What is claimed is:
 1. A fuel injection system for an internalcombustion engine, comprising: at least one fuel injector for injectinga fuel into a combustion chamber that is delimited by a cylinder wall inwhich a piston is guided; and a spark plug extending into the combustionchamber, wherein: the at least one fuel injector is configured toproduce a fuel-air mixture cloud in the form of a conical spray jet inthe combustion chamber, and the conical spray jet has an angle cutout inan area of the spark plug.
 2. The fuel injection system according toclaim 1, wherein: the spark plug is situated on an angle bisector of theangle cutout.
 3. The fuel injection system according to claim 2,wherein: an opening angle of the conical spray jet is between 60° and150°.
 4. The fuel injection system according to claim 1, wherein: anozzle body of the at least one fuel injector includes at least one rowof injection holes situated on a periphery.
 5. The fuel injection systemaccording to claim 4, wherein: the injection holes situated in the atleast one row on the periphery have an angular distance between themamounting to between 20° and 30° outside the angle cutout.
 6. The fuelinjection system according to claim 4, wherein: the injection holessituated on the periphery in a section facing the spark plug are spaceda greater distance apart than those over a remaining angular range. 7.The fuel injection system according to claim 6, wherein: the greaterspacing of the injection holes to form the angle cutout is between 30°and 60°.
 8. The fuel injection system according to claim 4, wherein: theinjection holes form two rows situated around the periphery.
 9. The fuelinjection system according to claim 8, wherein: the two rows of theinjection holes situated on the periphery are rotated with respect toone another about a common midpoint, so that the injection holes of afirst row of the two rows are situated on an angle bisector of theinjection holes of the second row of the two rows.
 10. The fuelinjection system according to claim 9, wherein: the two rows of theinjection holes situated on the periphery and rotated with respect toone another include the angle cutout in the area of the spark plug. 11.The fuel injection system according to claim 1, wherein: the mixturecloud is a substantially homogenous fuel-air mixture without leanpockets.
 12. The fuel injection system according to claim 1, wherein: aninjection rate of the jet is greatest at the center of the jet and onangle bisectors of two injection jets bordering the area of the sparkplug.
 13. The fuel injection system according to claim 1, wherein: themixture cloud is formed by first and second conical jet sprays, thefirst jet spray including an internal conical lateral surface and thesecond jet spray including an external conical lateral surface having acone angle higher than that of the first jet spray.
 14. The fuelinjection system according to claim 1, wherein: the fuel is not injecteddirectly against a surface of a cylinder head recess.
 15. A method ofinjecting a fuel into a combustion chamber of an internal combustionengine by using a fuel injector that is delimited by a cylinder wall inwhich a piston is guided, with a spark plug projecting into thecombustion chamber, the method comprising the step of: causing the fuelinjector to produce a fuel-air mixture cloud in the form of a conicalinjection jet that has an angle cutout in an area of the spark plug.